So I am running into an issue when I run a security scan on my application. It turns out that I am failing to protect against XXE.
Here is a short snippet showing the offending code:
static void Main()
{
string inp = Console.ReadLine();
string xmlStr = ""; //This has a value that is much too long to put into a single post
if (!string.IsNullOrEmpty(inp))
{
xmlStr = inp;
}
XmlDocument xmlDocObj = new XmlDocument {XmlResolver = null};
xmlDocObj.LoadXml(xmlStr);
XmlNodeList measureXmlNodeListObj = xmlDocObj.SelectNodes("REQ/MS/M");
foreach (XmlNode measureXmlNodeObj in measureXmlNodeListObj)
{
XmlNode detailXmlNodeListObj = xmlDocObj.SelectSingleNode("REQ/DTD");
string measureKey = measureXmlNodeObj.Attributes["KY"].Value;
if (detailXmlNodeListObj.Attributes["MKY"].Value ==
measureKey) //Checking if selected MeasureKey is same
{
XmlNode filerNode = measureXmlNodeObj.SelectSingleNode("FS");
if (filerNode != null)
{
XDocument fixedFilterXmlObj = XDocument.Load(new StringReader(filerNode.OuterXml));
var measureFixedFilters = (from m in fixedFilterXmlObj.Element("FS").Elements("F")
select m).ToList();
foreach (var fixedFilter in measureFixedFilters)
{
var fixedFilterValues = (from m in fixedFilter.Elements("VS").Elements("V")
select m.Attribute("DESC").Value).ToList();
foreach (var value in fixedFilterValues)
{
Console.WriteLine(value.Trim());
}
}
}
}
}
Console.ReadLine();
}
According to Veracode, the line that unsafe is XDocument fixedFilterXmlObj = XDocument.Load(new StringReader(filerNode.OuterXml));
But it seems like according to Owsap, it should be safe:
Both the XElement and XDocument objects in the System.Xml.Linq library
are safe from XXE injection by default. XElement parses only the
elements within the XML file, so DTDs are ignored altogether.
XDocument has DTDs disabled by default, and is only unsafe if
constructed with a different unsafe XML parser.
So it seems like I am making the mistake of using an usafe XML Parser, opening XDocument to XXE.
I found a unit test that replicates the issue and also has a safe usage of XDocument but I can't seem to find what exactly my code is unsafe, because I do not use:
XmlReaderSettings settings = new XmlReaderSettings();
settings.DtdProcessing = DtdProcessing.Parse; // unsafe!
You can run my code to replicate the issue, but you should replace the line with the empty xmlStr with this value: here (too large for a single post)
I'm not sure how or why this works, but it does:
XDocument fixedFilterXmlObj;
using (XmlNodeReader nodeReader = new XmlNodeReader(filerNode))
{
nodeReader.MoveToContent();
fixedFilterXmlObj = XDocument.Load(nodeReader);
}
Related
I have changed the code when trying to fix Veracode error for Improper Restriction of XML External Entity Reference, but it did not fix it.
Here is the code I have now:
XmlDocument xmlDoc=new XmlDocument();
using (System.IO.MemoryStream xmlstream = new System.IO.MemoryStream
(Encoding.Default.GetBytes(dsEQ.GetXml().ToString())))
{
XmlReaderSettings settings = new XmlReaderSettings();
settings.DtdProcessing = DtdProcessing.Prohibit;
using (XmlReader xmlreader = XmlReader.Create(xmlstream, settings))
{
try
{
xmlDoc.Load(xmlreader);
}
catch(XmlException e)
{
Connection.LogError(e.ToString(), e.Message);
}
}
}
However, Veracode still point out on this section of code with the same error message.
Is there anything else that I should do to fix it? We do not have any external references, everything is through intranet.
Set XmlResolver to null:
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.XmlResolver = null;
Set XmlResolver = null will fix the issue.
static void LoadXML()
{
string xml = "<?xml version=\"1.0\" ?><!DOCTYPE doc
[<!ENTITY win SYSTEM \"file:///C:/Users/user/Documents/testdata2.txt\">]
><doc>&win;</doc>";
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.XmlResolver = null; // Setting this to NULL disables DTDs - Its NOT null by default.
xmlDoc.LoadXml(xml);
Console.WriteLine(xmlDoc.InnerText);
Console.ReadLine();
}
Please go through below link for more information.
XML External Entity (XXE) Prevention Cheat Sheet
The original answer works for xmlDoc.Load(xmlreader).
The second question is a different context and requires different technology.
using (System.IO.StringReader rxml = new System.IO.StringReader(myxmltext))
{
XmlSerializer serializer = new XmlSerializer(typeof(MenuConfigBase));
using (XmlTextReader xr = new XmlTextReader(rxml))
{
xr.XmlResolver = null;
var cfgBase = (MenuConfigBase)serializer.Deserialize(xr);
}
}
I've read about all I could get on how to read from an XML file, but I can't get anything done. I want to read a connectionstring from an XML file, plain and simple, nothing more.
My XML looks like
<?xml version="1.0" standalone="yes"?>
<connectionString>
<conn>"adsf"</conn>
</connectionString>
And I've tried varios way with
XmlDocument doc = new XmlDocument();
XmlTextReader reader = new XmlTextReader(xmlLoc);
while (reader.MoveToNextAttribute())
{
XmlNode a = doc.ReadNode(reader);
textBox1.Text = Text + a.Name;
}
XmlDocument xml = new XmlDocument();
xml.LoadXml(xmlLoc); //myXmlString is the xml file in string //copying xml to string: string myXmlString = xmldoc.OuterXml.ToString();
XmlNodeList xnList = xml.SelectNodes("/connectionString");
foreach (XmlNode xn in xnList)
{
XmlNode example = xn.SelectSingleNode("conn");
if (example != null)
{
string na = example["Name"].InnerText;
string no = example["NO"].InnerText;
}
}
I'm missing something and I'm not sure what, this should be a very simple task, but I can't get it done. Any help?
I'm trying to do it in a WIndows form application program.
I'm missing something?
Yes. .NET has a built in mechanism for storing your connection string, inside an App.config file, there is no reason to manually store it and parse it yourself.
Right click your project, go to Add -> New Item
Then, add a "Application Configuration File":
Once it opens, add a connectionStrings node to it, as follows:
// This is an example of a connectionString node. You may add child
// values to it as follows
<connectionStrings>
<add name="YourConnectionStringKey"
providerName="System.Data.SqlClient"
connectionString="Data Source=.\SQLEXPRESS;Initial Catalog=YourDB;Trusted_Connection=Yes" />
</connectionStrings>
Then, you access it using ConfigurationManager.ConnectionStrings:
string connectionString =
ConfigurationManager.ConnectionStrings["YourConnectionStringKey"].ConnectionString;
You can use linq to xml.
var xmlStr = File.ReadAllText("fileName.xml");
var str = XElement.Parse(xmlStr);
var result = str.Elements("word").
Where(x => x.Element("connectionString").Value.Equals("conn"));
Console.WriteLine(result);
This might work (or may be some changes you need to make.
var x = XElement.Parse(#"<?xml version=""1.0"" standalone=""yes""?><connectionString><conn>adsf</conn></connectionString>");
// or var x = XElement.Load(#"c:\temp\my.xml");
var s = x.Element("conn").Value;
If you still have not found your answer then try this (a bit old school but it worked for me)
public class Common
{
public Common()
{
}
// public static string GetXML()
// {
// return #"C:\MyLocation\Connections.xml";
// }
public static string GetXMLconn(string strConn)
{
string xmlConStr = "";
//
string XMLconn = #"C:\Mylocation\Connections.xml";
// Get the Connection String from the XML file.
XmlTextReader textReader = new XmlTextReader(XMLconn);
textReader.Read();
while (textReader.Read())
{
// Read the currect element in the loop
textReader.MoveToElement();
// If the element name is correct then read and assign the connection string
if (textReader.Name == strConn)
{
xmlConStr = textReader.ReadString();
}
}
textReader.Close();
return xmlConStr;
}
}
I'm trying to call a method from a catch block but the xmlnode inside the method doesn't seem to work. I'm getting a null. If I call the same method from the try block it works.
var doc = new XmlDocument();
try
{
doc.Load(f.FullPath);
// do some work
}
catch (Exception e)
{
if (e is XMLException)
{
checkXML(ref doc);
}
public void checkXML(ref XmlDocument doc)
{
XmlNode xn = doc.SelectSingleNode("/BroadcastMonitor/Current");
xn["name1"].InnerText = SecurityElement.Escape(xn["name1"].InnerText);
xn["name2"].InnerText = SecurityElement.Escape(xn["name2"].InnerText); ;
}
Now when the catch block calls method 'checkXML', i get xn as null. But if I execute the same from the 'try' block just to check, 'xn' has a value. 'doc' too has a value regardless of when called try or from catch block.
Why is this happening? Please help me understand.
EDIT
<BroadcastMonitor>
<updated>2014-10-17T07:56:30</updated>
<Name>TESTING</Name>
<Current>
<artistName>اصاله& نصرى</artistName>
<albumName>شخصيه عنيده</albumName>
<CategoryName>ARABIC & SONGS</CategoryName>
</Current>
</BroadcastMonitor>
Thank you.
Your xml contains an & character which is not a 'valid' xml character and must be escaped.
<CategoryName>ARABIC & SONGS</CategoryName>
So it's causing your Load() method to throw the exception.
What you should do is escape all the invalid characters in your xml string before passing them on to an xml parser like so
yourXmlString = XmlConvert.EncodeName(yourXmlString);
You can then pass the yourXmlString on to the parser like so
var xDoc = XDocument.Parse(yourXmlString);
or if you don't want to or can't use the XDocument class you will need to make sure you save the xml encoded so that the Load() method of the XmlDocument class will be reading a file that is properly encoded.
Note that XmlDocument and XDocument classes are not the same thing and have some significant differences. Method Parse(), if I remember correctly, is one of the advantages that XDocument has over XmlDocument.
EDIT :
You can read the xml file into a string using the File class
var yourXmlString = File.ReadAllText(filePath);
XmlDocument is a reference type... no need to pass it with ref.
And my guess is that its failing to load in the first place so doc is really null
It looks like this document is missing its xml declaration tag.
try:
XmlDocument doc = new XmlDocument;
using(StreamReader reader = new StreamReader(f.FullPath))
{
doc.LoadXml(reader.ReadToEnd());
}
You can use System.IO.File.ReadAllText() to get all text from file into a string variable :
string invalidXml = System.IO.File.ReadAllText(f.FullPath);
For this particular XML, you can simply replace & with it's encoded version & to make a valid XML string :
string validXml = invalidXml.Replace("&", "&");
doc.LoadXml(validXml);
.....
Related question for reference : Reading XML with an "&" into C# XMLDocument Object
This would be my solution:
private static Regex InnerValues = new Regex(#"(?<=<(.*?>)).*?(?=</\1)",RegexOptions.Compiled);
private static XmlDocument LoadInvalidDocument(string path)
{
XmlDocument result = new XmlDocument();
string content = File.ReadAllText(path);
var matches = InnerValues.Matches(content);
foreach (Match match in matches)
{
content = content.Replace(match.Value, HttpUtility.HtmlEncode(match.Value));
}
result.LoadXml(content);
return result;
}
I am building a Windows 8 app, and I need to extract the whole XML node and its children as string from a large xml document, and the method that does that so far looks like this:
public string GetNodeContent(string path)
{
XmlReaderSettings settings = new XmlReaderSettings();
settings.IgnoreWhitespace = true;
settings.ConformanceLevel = ConformanceLevel.Auto;
settings.IgnoreComments = true;
using (XmlReader reader = XmlReader.Create("something.xml", settings))
{
reader.MoveToContent();
reader.Read();
XmlDocument doc = new XmlDocument();
doc.LoadXml(reader.ReadOuterXml());
IXmlNode node = doc.SelectSingleNode(path);
return node.InnerText;
}
}
When I pass any form of xpath, node gets the value of null. I'm using the reader to get the first child of root node, and then use XMLDocument to create one from that xml. Since it's Windows 8, apparently, I can't use XPathSelectElements method and this is the only way I can't think of. Is there a way to do it using this, or any other logic?
Thank you in advance for your answers.
[UPDATE]
Let's say XML has this general form:
<nodeone attributes...>
<nodetwo attributes...>
<nodethree attributes... />
<nodethree attributes... />
<nodethree attributes... />
</nodetwo>
</nodeone >
I expect to get as a result nodetwo and all of its children in the form of xml string when i pass "/nodeone/nodetwo" or "//nodetwo"
I've come up with this solution, the whole approach was wrong to start with. The problematic part was the fact that this code
reader.MoveToContent();
reader.Read();
ignores the namespace by itself, because it skips the root tag. This is the new, working code:
public static async Task<string> ReadFileTest(string xpath)
{
StorageFolder folder = await Package.Current.InstalledLocation.GetFolderAsync("NameOfFolderWithXML");
StorageFile xmlFile = await folder.GetFileAsync("filename.xml");
XmlDocument xmldoc = await XmlDocument.LoadFromFileAsync(xmlFile);
var nodes = doc.SelectNodes(xpath);
XmlElement element = (XmlElement)nodes[0];
return element.GetXml();
}
I have a piece of code which works well for normal files. But for really big files, it makes the server stop working.
Here it is:
XmlReader reader = null;
try
{
reader = XmlReader.Create(file_name + ".xml");
XDocument xml = XDocument.Load(reader);
XmlNamespaceManager namespaceManager = GetNamespaceManager(reader);
XElement root = xml.Root;
//XAttribute supplier = root.XPathSelectElement("//sh:Receive/sh:Id", namespaceManager).Attribute("Authority");
//string version = root.XPathSelectElement("//sh:DocumentId/sh:Version", namespaceManager).Value;
var nodes = root.XPathSelectElements("//eanucc:msg/eanucc:transact", namespaceManager);
return nodes;
}
catch
{ }
I think this is the part which causes the memory problem which happens on the server. How can I fix this?
It sounds like there's simply too much data to read in one go. You'll have to iterate over the elements one at a time, using XmlReader as a cursor, and converting one element to XElement at a time.
public static IEnumerable<XElement> ReadTransactions()
{
using (var reader = XmlReader.Create(file_name + ".xml"))
{
while (reader.ReadToFollowing("transact", eanuccNamespaceUri))
{
using (var subtree = reader.ReadSubtree())
{
yield return XElement.Load(subtree);
}
}
}
}
Note: this assumes there are never "transact" elements at any other level. If there are, you'll need to be more careful with your XmlReader than just calling ReadToFollowing. Also note that you'll need to find the actual namespace URI of the eanucc alias.
Don't forget that if you try to read all of this information in one go (e.g. by calling ToList()) then you'll still run out of memory. You need to stream the information. (It's not clear what you're trying to do with the elements, but you need to think about it carefully.)
Try putting the reader in a using(){} clause so it gets disposed of after use.
try
{
using(var reader = XmlReader.Create(file_name + ".xml"))
{
XDocument xml = XDocument.Load(reader);
XmlNamespaceManager namespaceManager = GetNamespaceManager(reader);
XElement root = xml.Root;
var nodes = root.XPathSelectElements("//eanucc:msg/eanucc:transact", namespaceManager);
return nodes;
}
}
catch
{ }